1. Field of the Invention
This invention relates generally to the casting of a diafram (aka. diaphragm) for use in steam turbines, gas turbines, and expanders.
2. Description of Related Art
A diafram is a critical part in the flow path of steam turbines, gas turbines, and expanders. A diafram is a structure comprising an inner ring (smaller diameter) and an outer ring (larger diameter) that supports radial, or nearly radial, vanes captured at their inner and outer radial ends and substantially uniformly circumferentially spaced. Axial flow directed through the vane passages (area between the endwall of the rings and the vanes) converts thermal energy to kinetic energy that imparts angular momentum to the turbine rotor to create mechanical power. The turbine transfers fluid thermal energy to the driven equipment with which it is associated. These diaframs are typically manufactured by welding airfoil-shaped preformed vanes into inner and outer rings, or by casting preformed vanes into inner and outer rings. However, this casting process relies on complex patterns and core construction tools to properly position the vanes within the diafram, and these patterns and core building tools are not precise and wear over time. As a result, the location and orientation of the vanes in the cast diafram core are not precisely controlled. Any deviation in the location and/or orientation of the vane causes a deviation in the vane throat area, which substantially controls the fluid flowrate and affects the quality of energy transfer. Therefore, precise control of the vane position and orientation is critical in order to meet performance requirements for flowrate and power.
The technology allowing more precise positioning of the diafram vanes in the casting core is termed “three-dimensional printing.” It is already part of rapid casting technology and is disclosed in U.S. Pat. Nos. 5,204,055 and 6,146,567. As described in these patents, a three-dimensional component can be created by bonding together successive layers of a porous material with droplets of a binder material. A multiple array of on-off controlled nozzles is scanned over the surface of a bed of porous material in multiple passes using an interlacing of the printed lines which deposit the binder thereon. This method enables the creation of three-dimensional sand cores built in a layer-wise fashion.